Refactoring exercise #1

models.rb

class Price 
  def price_code; end
  def charge; end
  def frequent_renter_points
    1
  end
  
  class Childrens
    def price_code; Movie::CHILDRENS; end
    def charge(days_rented)
      result = 1.5;
      if days_rented > 3
        result = result + (days_rented - 3) * 1.5
      end
      return result
    end
  end
  
  class NewRelease
    def price_code; Movie::NEW_RELEASE; end
    def charge(days_rented)
      result = days_rented * 3
    end
    def frequent_renter_points
      days_rented > 1 ? 2 : 1
    end
  end
  
  class RegularPrice
    def price_code; Movie::REGULAR; end
    def charge(days_rented)
      result = 2;
      if days_rented > 2
        result = result + (days_rented - 2) * 1.5
      end
      return result
    end
  end
end

class Movie < ActiveRecord::Base
  has_many :rentals
  
  CHILDRENS = 2
  REGULAR = 0
  NEW_RELEASE = 1
  
  attribute :title, :string
  attribute :price_code, :int
  
  attr_accessor :price
  
  def initialize
    case price_code
    when REGULAR
      @price = Price::Regular.new
    when CHILDRENS
      @price = Price::Childrens.new
    when NEW_RELEASE
      @price = Price::NewRelease.new
    end
  end
  
  def price_code
    @price.price_code
  end
  
  def frequent_renter_points(days_rented)
    @price.frequent_renter_points(days_rented)
  end
  
  def charge(days_rented)
    @price.charge(days_rented)
  end
end

class Rental < ActiveRecord::Base
  belongs_to :movie
  belongs_to :customer
  
  attribute :days_rented, :int
  
  def frequent_renter_points 
    movie.frequent_rental_points(days_rented)
  end
  
  def charge
    movie.charge(days_rented)
  end
end

class Customer < ActiveRecord::Base
  has_many :rentals
  
  attribute :name, :string
  
  def total_charge
    rentals.map(&:charge).sum
  end
  
  def total_frequent_renter_points
    rentals.map(&:frequent_renter_points).sum
  end
  
  def statement 
      result = "Rental Record for #{name} \n"
    
      rentals.for_each { |rental|        
        result << "\t#{rental.movie.title}\t#{rental.charge}\n"
      }
    
      result << "Amount owed is #{total_charge}\n"
      result << "You earned #{total_frequent_renter_points} frequent renter points"
      return total_amount
  end
end 

Play though the Gist Revisions to see each refactoring step

Tried to refactor the piece of code introduced in the opening chaper of Refactoring: Improving the Design of Existing Code by Martin Folwer. It was originally in Java, I've tried to follow the exercise in Ruby.

Techniques used here

• Extract Method
• Move Method
• Replace Conditional with Polymorphism
• Replace Type Code with State
• Delegation